The invention relates to a reservoir-type fuel injection system, in which fuel can be delivered under pressure to a reservoir, having a line carrying pressure fuel under pressure from the reservoir via a valve assembly to at least one injection nozzle, and having an adjustable throttle to vary the quantity of fuel supplied to the reservoir.
In reservoir fuel injection systems of the types described above, a pressure reservoir is supplied with fuel under pressure from a continuously pumping charge pump; a check valve is provided between the charge pump and the pressure reservoir to prevent fuel from being forced back into the pump under pressure in the intake stroke of the pump. Reservoir fuel injection systems consequently require control devices, which monitor the quantity and timing of the further delivery of the fuel under pressure to the injection nozzle; rotating distributor shafts and/or valve assemblies, in particular magnetic valves, are used for this purpose. In typical reservoir fuel injection systems of the type described at the outset above, there is no particular regulation of the charge pump; provision is merely made so that the charge pump will pump a sufficient quantity of fuel into the reservoir, which prevents the ability to completely evacuate the reservoir, particularly at high rpm.
In such reservoir fuel injection systems, particularly in engine overrunning, a substantially higher pump feed quantity encounters a withdrawal of fuel from the reservoir that may extend to zero. Adapting the feed quantity of the pump to the requirement, with certain limitations, has already been proposed in U.S. Pat. No. 4,572,136. In this known system a pressure reservoir was used, the reservoir piston of which has a circumferential groove that upon displacement of the reservoir piston represents a variably great, throttle resistance in the intake line of the charge pump. However, in this known system, the governing functions only as long as the withdrawal from the reservoir does not proceed definitively to zero, as is the case for instance in engine overrunning, because in these cases the intake line is overtaken entirely and blocked by the known piston embodiment. As a consequence, the pump can run dry, because no further fuel is supplied to it via the intake line, and the intake line is completely closed. In any event, such an embodiment leads to increased pump wear and to a shortening of its service life; particularly with feed quantities tending to zero, the consequence may be destruction of the pump, and particularly of the tightness properties of the pump.